One last example

Before we finish this chapter, we'll show you a simple problem that Fabrizio used to submit to candidates for a Python developer role in a company he used to work for.

The problem is the following: write a function that returns the terms of the sequence 0 1 1 2 3 5 8 13 21 ..., up to some limit, N.

If you haven't recognized it, that is the Fibonacci sequence, which is defined as F(0) = 0, F(1) = 1 and, for any n > 1, F(n) = F(n-1) + F(n-2). This sequence is excellent for testing knowledge about recursion, memoization techniques, and other technical details, but in this case, it was a good opportunity to check whether the candidate knew about generators.

Let's start with a rudimentary version, and then improve on it:

# fibonacci.first.py
def fibonacci(N):
    """Return all fibonacci numbers up to N. """
    result = [0]
    next_n = 1
    while next_n <= N:
        result.append(next_n)
        next_n...